Almost all major template for JS frameworks these days include that line. And there are tons of guides that specify adding that in.

I get why it's there, if you're building a PWA that is supposed to mimick a mobile app, you have to enable that to override some annoying mobile browser behaviors like zooming on an input.

The problem is that the above scenario is about the only time you would want to set the viewport in that way. Yet because the line gets included in boilerplates to make it easier to make PWA's, it ends up in a ton of stuff that definitely is not a PWA and should not have that.